The present invention relates to a family of power transmissions having two input clutches which selectively connect an input shaft to first and second pairs of planetary gear sets to provide at least five forward speed ratios and one reverse speed ratio.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times.
A primary focus of transmission and engine design work is in the area of increasing vehicle fuel efficiency. Manual transmissions typically provide improved vehicle fuel economy over automatic transmissions because automatic transmissions use a torque converter for vehicle launch and multiple plate hydraulically-applied clutches for gear engagement. Clutches of this type, left unengaged or idling, impose a parasitic drag torque on a drive line due to the viscous shearing action which exists between the plates and discs rotating at different speeds relative to one another. This drag torque adversely affects fuel economy for automatic transmissions. Also, the hydraulic pump that generates the pressure needed for operating the above-described clutches further reduces fuel efficiency associated with automatic transmissions. Manual transmissions eliminate these problems.
While manual transmissions are not subject to the above described fuel efficiency related problems, manual transmissions typically provide poor shift quality because a significant torque interruption is required during each gear shift as the engine is disengaged from the transmission by the clutch to allow shafts rotating at different speeds to be synchronized.
So called xe2x80x9cautomated manualxe2x80x9d transmissions provide electronic shifting in a manual transmission configuration which, in certain circumstances, improves fuel efficiency by eliminating the parasitic losses associated with the torque converter and hydraulic pump needed for clutching. Like manual transmissions, a drawback of automated manual transmissions is that the shift quality is not as high as an automatic transmission because of the torque interruption during shifting.
So called xe2x80x9cdual-clutch automaticxe2x80x9d transmissions also eliminate the torque converter and replace hydraulic clutches with synchronizers but they go further to provide gear shift quality which is superior to the automated manual transmission and similar to the conventional automatic transmission, which makes them quite attractive. However, most known dual-clutch automatic transmissions include a lay shaft or countershaft gear arrangement, and have not been widely applied in vehicles because of their complexity, size and cost. For example, a dual clutch lay shaft transmission could require eight sets of gears, two input/shift clutches and seven synchronizers/dog clutches to provide six forward speed ratios and a reverse speed ratio. An example of a dual-clutch automatic transmission is described in U.S. Pat. No. 5,385,064, which is hereby incorporated by reference.
The invention provides a low content multi-speed dual-clutch transmission family utilizing planetary gear sets rather than lay shaft gear arrangements. In particular, the invention includes four planetary gear sets, two input/shift clutches, and eight selectable torque transmitting mechanisms to provide at least six forward speed ratios and a reverse speed ratio.
According to one aspect of the invention, the family of transmissions has four planetary gear sets, each of which includes a first, second and third member, which members may comprise a sun gear, ring gear, or a planet carrier assembly member.
In referring to the first, second, third and fourth gear sets in this description and in the claims, these sets may be counted xe2x80x9cfirstxe2x80x9d to xe2x80x9cfourthxe2x80x9d in any order in the drawings (i.e. left-to-right, right-to-left, etc.).
In another aspect of the present invention, each of the planetary gear sets may be of the single pinion type or of the double pinion type.
In yet another aspect of the present invention, the first member of the first planetary gear set is continuously connected with a stationary member (transmission housing).
In yet another aspect of the present invention, the first member of a second planetary gear set is continuously connected with the first member of the third planetary gear set and with the output shaft through a first interconnecting member.
In yet another aspect of the present invention, the first member of the fourth planetary gear set is continuously connected with a stationary member (transmission housing).
In yet another aspect of the present invention, in some cases, a member of the first planetary gear set is continuously connected with a member of the second planetary gear set through a second interconnecting member.
In accordance with a further aspect of the invention, a first input clutch selectively connects the input shaft with a member of the first or second planetary gear set.
In accordance with another aspect of the present invention, a second input clutch selectively connects the input shaft with the second member of the third planetary gear set.
In another aspect of the invention, first, second, third and fourth torque transmitting mechanisms, such as synchronizers, selectively connect members of the first and second planetary gear sets with other members of the first and second planetary gear sets, or with the first input clutch.
In still a further aspect of the invention, fifth, sixth, seventh and eighth torque transmitting mechanisms, such as synchronizers, selectively connect members of the third and fourth planetary gear sets with other members of the third and fourth planetary gear sets.
In accordance with a further aspect of the invention, the input clutches and torque transmitting mechanisms are selectively engaged in combinations of at least two to provide at least six forward speed ratios and a reverse speed ratio.
In accordance with a further aspect of the invention, the first input clutch is applied for odd number speed ranges, and the second input clutch is applied for even number speed ranges, or vice versa.
In another aspect of the invention, the first input clutch and the second input clutch are interchanged (i.e. alternately engaged) to shift from odd number speed range to even number speed range, or vice versa.
In accordance with a further aspect of the invention, each selected torque transmitting mechanism for a new speed ratio is engaged prior to shifting of the input clutches to achieve shifts without torque interruptions.
In accordance with a further aspect of the invention, at least one pair of synchronizers is executed as a double synchronizer to reduce cost and package size.
In accordance with a further aspect of the invention, in some cases at least one of the torque transmitting mechanisms can be eliminated to realize five forward speed ratios and a reverse speed ratio.